A pipe-connecting device using an inner ring is configured by: a tubular screwing portion which is projected from a pipe joint body or a fluid apparatus in a state where an external thread is formed on the outer circumference; a seal inner ring in which an annular large-diameter portion is raised on the radially outward side; and a union nut in which an internal thread to be screwed with the external thread is formed. For example, the pipe-connecting device disclosed in Patent Literature 1 is known.
The pipe-connecting device disclosed in Patent Literature 1 includes: a tubular screwing portion which is disposed in a pipe joint body in a state where an external thread is formed on the outer circumference; an inner ring in which an inner circumferential portion is formed as a fluid passage, and an annular large-diameter portion is raised on the radially outward side, and which is used for fixing a pipe; and a union nut in which an internal thread to be screwed with the external thread is formed.
In the above-described pipe-connecting device, when a tube is to be connected to the pipe joint body, the inner ring is firstly press-inserted into an end portion of the tube from an opening of the tube, and the end portion of the tube is flared and deformed by the annular large-diameter portion. Next, the tube which is flared and deformed, and which has the inner ring is inserted into the tubular screwing portion.
Next, the internal thread of the union nut is screwed with the external thread of the tubular screwing portion. Then, the union nut is fastened and crew-advanced, and this screw advancement causes the union nut to press the tube having the inner ring in the axial direction, thereby performing the connection of the tube.
In a pipe-connecting device such as the above-described one, means was employed which is based on the concept that the union nut is fastened to strongly press the flared portion of the tube in the axial direction to a degree by which the portion is recessed, by the seal pressing portion (see the pressing edge 3C in Patent Literature 1) that is a pointed place, thereby performing a sealing function.
In order to ensure the seal performance and the security against the slipping off of the tube, namely, a strong fastening work using a tool is required. Therefore, there are difficulties such as a large burden on the worker, a difficulty of a work in a confined space, and occurrence of working variation. In some cases, there is a possibility that the performance may be affected by insufficient fastening.
Moreover, strong fastening causes large stress to be applied to various portions, and the deformation is increased. In order to prevent loosening due to a long-term use or a use at a high temperature from occurring, therefore, a refastening operation is sometimes performed. In the case where detachment or reconstruction is performed in accordance with component replacement or maintenance, it is necessary to conduct the fastening operation at a degree which is higher than that of the previous fastening operation. In a conventional pipe-connecting device, therefore, there remains room for improvement in repeated uses, such as that the fastening position or the number of uses is often limited, and that, in a place where detachment is frequently performed, component replacement must be immediately performed.